The corrosion of metal degrades iron-based tools and structures presents a challenging problem to industries worldwide. When metals come in contact with different environments such as air, water, chemical products, and pollutants, they begin to degrade as a result of the metal interacting with its environment. For example, rusting is the loss of electrons from metals reacting with water and oxygen. This type of electrochemical corrosion causes severe damage to industrial equipment, materials, and buildings.
Current corrosion control measures include non-electrochemical means by galvanizing metal with an inexpensive metallic element. Typically, the galvanization process coats steel with zinc. Additionally, there are electrochemical means of protecting metal from corrosion via a cathodic protection wherein the metal to be protected acts as a cathode and is in electrochemical contact with another more corrosive metal acting as an anode. However, these measures have the disadvantage of being costly measure for controlling corrosion. The adoption of preventive measures that reduce or eliminate corrosion is financially costly and time consuming. The National Institute of Standards and Technology (NIST) estimated in 1996 that the cost of corrosion for the United States is over $300 billion. Given high cost of corrosion control there is a need to explore other corrosion control methods.
Other corrosion protection control means include applying a protective paint or epoxy coating to form a physical barrier between the metal surface from oxidizing with oxygen. The measure of applying a protective coating on metals has the advantage that the coating can be applied post-manufacturing of the metal. However, using such a protective coating has the drawback of necessitating constant maintenance through re-application inasmuch as a rupture in the coating allows for localized corrosion to occur under the protective coat and ultimately disputes the protective coating. Ideally, a protective coating would have self-healing properties and would not require re-application or minimize re-application.
Microbial populations have been observed to both increase as well as decrease the rate of metal corrosion. As detailed in Jayaramna et al., 1997, Journal of Industrial Microbiology & Biotechnology, 18, 396-401, cultures of bacterial species of Pseudomonas sp., Bacillus sp., and Hafnia alvei, have induced corrosion of mild steel. On the other hand, cultures of aerobic bacteria species Pseudomonans S9 and Serratia marscens EF190 have been shown to confer a 10-fold corrosion inhibition of SIS 1146 steel. See Pedersen et al., 1989, Biofouling 1:313-322. Additionally, it has been reported that bacteria species Pseudomonas fragi and Escherichia coli DH5α(pKMY319) conferred corrosion protection of mild steel in a LB medium. See Jayaraman, et al., 1997, App Microbiol Biotechnol, 47:62-68. In these cases, the metal was submerged in an aqueous medium inoculated by a bacterial species. The bacteria colonized the metal substrate and excreted a heterogeneous exopolysaccharide adhering to metal surfaces facilitated by the functional groups of the exopolymer substance.
Various bacteria, such as Leuconostoc sp., produce exopolysaccharides into their surroundings. As disclosed in WO 03/008618, an α-1,6 glucan produced by Lactobacillus strain LMG P-20349 during the growth phase conferred anticorrosion properties to plain carbon steel sheets that were exposed to slightly corrosive medium of 0.1M LiClO4. The treated sheet with the Lactobacillus strain produced exopolysaccharide left a thin black layer, whereas the control and sheets covered with an exopolysaccharide from Lactobacillus sake displayed corrosion and localized corrosion respectively. Given the differences in anticorrosion properties of exopolysaccharides produced by different bacteria strains, there is a need in the art to determine as to which exopolysaccharides provide corrosion inhibition properties.